1. Field of the Invention
The invention relates to a multi-stage scanning method for increasing a scanning speed and enhancing an image quality, and more particularly to a multi-stage scanning method for lengthening an accelerating distance of an optical module in a scanner so as to increase the scanning speed and enhance the image quality.
2. Description of the Related Art
FIG. 1 is a schematic illustration showing a conventional book scanner 1. Referring to FIG. 1, the book scanner 1 has a transparent platen 2 and an inclined plane 4 connected to the transparent platen 2 to form a ridge 3. The ridge 3 supports an opened book 5, and the ridge 3 is far away from a start position P1 of an optical module 10 and close to an end position P6 of the optical module 10.
FIG. 2 shows movement stages of the optical module when the conventional book scanner of FIG. 1 is scanning a book. As shown in FIGS. 1 and 2, the conventional scanning method includes the following steps S101 to S104.
In step S101, the optical module 10 is moved, in a forward direction, from the start position P1 to the end position P6.
In step S102, the optical module 10 is accelerated and moved, in a reverse direction, from the end position P6 to a forward-boundary position P5 such that the optical module 10 has a speed V.
In step S103, the optical module 10 is moved at the speed V such that the optical module 10 can scan the book 5 to obtain an image until it reaches a reverse-boundary position P2.
In step S104, the optical module 10 is moved from the reverse-boundary position P2 back to the start position P1. In this step, the moving speed of the optical module 10 is usually higher than the speed V, such that the time for one scanning process is shortened.
The forward-boundary position P5 in the book scanner 1 is preferably close to the end position P6 such that the contents close to the inner ridge side of the book can be acquired. However, it is more difficult to accelerate the optical module 10 to the speed V if the distance from the position P6 to the position P5 is shorter. In this condition, a motor with a larger output torsional force has to be used to move the optical module 10, and the cost is thus high. Alternatively, even though the motor with the larger torsional force is used to move the optical module 10, the optical module 10 still cannot be moved at the stable speed V after the position P5 and the image quality is inevitably deteriorated if the distance from the position P6 to the position P5 is too short. In other words, if the scanning speed has to be increased without changing the motor, the period of time the optical module 10 is kept unstable will be longer and the image quality of the document edge is thus influenced.
FIG. 3 shows movement stages of the optical module when the conventional book scanner of FIG. 1 is scanning a document. The movement stages are also suitable for the typical flatbed scanner for scanning the document, so the conventional flatbed scanner will be no longer depicted and the reference may be made according to FIG. 1.
As shown in FIGS. 3 and 1, the conventional scanning method includes the following steps.
In step S201, the optical module 10 is accelerated and moved, in a forward direction, from a start position P1 to a reverse-boundary position P2 such that the optical module 10 has a speed V.
In step S202, the optical module 10 is enabled to scan a document at the speed V to obtain an image until the optical module 10 reaches a forward-boundary position P5.
In step S203, the optical module 10 is moved from the forward-boundary position P5 and stopped at an end position P6.
In step S204, the optical module 10 is moved from the end position P6 back to the start position P1 and then stopped. Because no scanning function is performed in this step, the speed of the optical module 10 can be increased to shorten the time for one scanning stroke.
However, the distance from the position P1 to the position P2 is gradually shortened in order to reduce the size of the scanner. Thus, the problem of insufficient accelerating distance, which is encountered in the scanning process of FIG. 2, still exists.